Ceramic composition having dispersion of nano-particles therein and methods of fabricating same

ABSTRACT

Ceramic compositions having a dispersion of nano-particles therein and methods of fabricating ceramic compositions having a dispersion of nano-particles therein are described. In an example, a method of forming a composition having a dispersion of nano-particles therein includes forming a mixture of semiconductor nano-particles and ceramic precursor molecules. A ceramic matrix is formed from the ceramic precursor molecules. The ceramic matrix includes a dispersion of the semiconductor nano-particles therein. In another example, a composition includes a medium including ceramic precursor molecules. The medium is a liquid or gel at 25 degrees Celsius. A plurality of semiconductor nano-particles is suspended in the medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of and claims the benefit of U.S.patent application Ser. No. 13/713,657 filed Dec. 13, 2012, the entirecontents of which are hereby incorporated by reference herein.

TECHNICAL FIELD

Embodiments of the present invention are in the field of quantum dotsand, in particular, ceramic compositions having a dispersion ofnano-particles therein and methods of fabricating ceramic compositionshaving a dispersion of nano-particles therein.

BACKGROUND

Quantum dots having a high photoluminescence quantum yield (PLQY) may beapplicable as down-converting materials in down-convertingnano-composites used in solid state lighting applications.Down-converting materials are used to improve the performance,efficiency and color choice in lighting applications, particularly lightemitting diodes (LEDs). In such applications, quantum dots absorb lightof a particular first (available or selected) wavelength, usually blue,and then emit light at a second wavelength, usually red or green.

SUMMARY

Embodiments of the present invention include ceramic compositions havinga dispersion of nano-particles therein and methods of fabricatingceramic compositions having a dispersion of nano-particles therein.

In an embodiment, a method of forming a composition having a dispersionof nano-particles therein includes forming a mixture of semiconductornano-particles and ceramic precursor molecules. A ceramic matrix isformed from the ceramic precursor molecules. The ceramic matrix includesa dispersion of the semiconductor nano-particles therein.

In another embodiment, a method of applying a light-conversion layer toa surface of a light-emitting diode (LED) includes forming a ceramicmatrix from a mixture of quantum dots and ceramic precursor molecules.The ceramic matrix includes a dispersion of the quantum dots therein.The ceramic matrix is applied to the surface of the LED.

In another embodiment, a method of applying a light-conversion layer toa surface of a light-emitting diode (LED) includes applying a mixture ofquantum dots and ceramic precursor molecules to the surface of the LED.A ceramic matrix is formed from the mixture, on the surface of the LED.The ceramic matrix includes a dispersion of the quantum dots therein.

In another embodiment, a composition includes a medium including ceramicprecursor molecules. The medium is a liquid or gel at 25 degreesCelsius. A plurality of semiconductor nano-particles is suspended in themedium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the conversion of a composition to a matrixincluding a dispersion of semiconductor structures, such as quantumdots, therein, in accordance with an embodiment of the presentinvention.

FIG. 2 illustrates a reaction pathway where a polysiloxane matrix isformed by ring-opening of cyclic monomers, such as cyclosiloxanes, inaccordance with an embodiment of the present invention.

FIG. 3A is a schematic of a hydration reaction of metal alkoxidemolecules to provide an active species, in accordance with an embodimentof the present invention.

FIG. 3B is a schematic of a condensation reaction of the active speciesof FIG. 3A to provide a condensed active species, in accordance with anembodiment of the present invention.

FIG. 3C is a schematic of a sol formation reaction of the condensedactive species of FIG. 3B to provide a polycondensed sol active species,in accordance with an embodiment of the present invention.

FIG. 3D is a schematic of cross-linking reactions of the polycondensedsol active species of FIG. 3C to provide a gel, in accordance with anembodiment of the present invention.

FIG. 4 is a schematic of reactions involving the formation of a ceramicmatrix of an infinite inorganic network as formed from linear ceramicprecursor molecules, in accordance with an embodiment of the presentinvention.

FIG. 5 illustrates a schematic of a cross-sectional view of a quantumdot suitable for dispersion in a composition or composition precursor,in accordance with an embodiment of the present invention.

FIG. 6 illustrates a cross-sectional view of a semiconductor structurehaving a nano-crystalline core and nano-crystalline shell pairing withone compositional transition layer, in accordance with an embodiment ofthe present invention.

FIG. 7 illustrates a cross-sectional view of a semiconductor structurehaving a nano-crystalline core/nano-crystalline shell/nano-crystallineouter shell combination with two compositional transition layers, inaccordance with an embodiment of the present invention.

FIG. 8 illustrates a cross-sectional view of a semiconductor structurehaving a nano-crystalline core/nano-crystalline shell/nano-crystallineouter shell combination with one compositional transition layer, inaccordance with an embodiment of the present invention.

FIG. 9 illustrates operations in a reverse micelle approach to coating asemiconductor structure, in accordance with an embodiment of the presentinvention.

FIG. 10 illustrates a lighting device that includes a blue LED with alayer having a composition with a dispersion of quantum dots therein, inaccordance with an embodiment of the present invention.

FIG. 11 illustrates a cross-sectional view of a lighting device with alayer having a composition with a dispersion of quantum dots therein, inaccordance with an embodiment of the present invention.

FIG. 12 illustrates a cross-sectional view of a lighting device with alayer having a composition with a dispersion of quantum dots therein, inaccordance with another embodiment of the present invention.

FIG. 13 illustrates a cross-sectional view of a lighting device with alayer having a composition with a dispersion of quantum dots therein, inaccordance with another embodiment of the present invention.

FIG. 14 illustrates a cross-sectional view of a lighting device with alayer having a composition with a dispersion of quantum dots therein, inaccordance with another embodiment of the present invention.

FIGS. 15A-15C illustrate cross-sectional views of various configurationsfor lighting devices with a layer having a composition with a dispersionof quantum dots therein, in accordance with another embodiment of thepresent invention.

DETAILED DESCRIPTION

Ceramic compositions having a dispersion of nano-particles therein andmethods of fabricating ceramic compositions having a dispersion ofnano-particles therein are described herein. In the followingdescription, numerous specific details are set forth, such as specificquantum dot geometries and efficiencies, in order to provide a thoroughunderstanding of embodiments of the present invention. It will beapparent to one skilled in the art that embodiments of the presentinvention may be practiced without these specific details. In otherinstances, well-known related apparatuses, such as the host of varietiesof applicable light emitting diodes (LEDs), are not described in detailin order to not unnecessarily obscure embodiments of the presentinvention. Furthermore, it is to be understood that the variousembodiments shown in the figures are illustrative representations andare not necessarily drawn to scale.

One or more embodiments described herein are directed to improvementsfor quantum dot (QD) performance by fabrication of thin films with highloadings of QDs therein for solid state lighting, such as light emittingdiodes (LEDs). Other applications of such films can include uses inother LED applications, photovoltaics, sensing, photonics, andbiotechnology.

To provide context, while integrating QDs into a silicone matrix hasbeen pursued as a competitive drop-in replacement for phosphors, somelimitations of silicones can be a barrier to such applications.Limitations such as difficulty in high loading of inorganicnanostructures per unit mass polymer, lack of homogeneousdispersibility, and inhibiting thermo-mechanical properties of thesilicones are examples significant hurdles to replacing phosphor basedmaterials with QD based materials. In particular, a significantchallenge has been to achieve a necessary high loading of QDs in a thinlayer (e.g., a layer having a thickness of approximately ca. 100microns), which can be deposited directly onto an LED device.

To address the above issues, one or more embodiments described hereininvolve integrating nano-particles (such as quantum dots) into aninfinite network such as cross-linked polymers or ceramics from smallmolecular or oligomeric (low molecular polymers) dispersions with lowviscosity. The low viscosity species are precursors for polymeric orother types of inorganic matrices. This general approach enables muchhigher loading of the QDs in the resulting QD containing applicationlayer or film. Furthermore, particle separation that can otherwiseresult in localized agglomeration of particles is avoided. In one suchembodiment, the use of a thin film prepared from a sol-gel materialincorporating QDs represents a departure from a silicone based polymermatrix and can be used together with an approach involving encapsulationof individual QDs with an insulator. The resulting system can ultimatelyexhibit increasing, rather than decreasing, photoluminescence (PL) ascorrelated with increasing temperature.

As elaborated below, some embodiments involve the use of quantum dothetero-structures (QDHs) dispersed in cyclic monomers (e.g.,cyclosiloxanes) with an intrinsic ability to open and polymerize in thepresence of an adequate initiator. Other embodiments, involve the use oforgano-ester alkoxide silsesquioxanes as relatively small molecularprecursors to silica. Both types of examples can have the advantage ofhigh metal content and low volatility. Additionally, polysilsesquioxanescan have the advantage of chemical versatility where a reactive organicmoiety may participate in a copolymerization reaction. Such an approachprovides control over mechanical properties through copolymerization.Also, silanol or other reactive groups may be included to participate inchemical reaction and the synthesis of cross-linked matrices. Oneprepared, or during preparation, the polymer matrices can be used forcoating an LED chip.

The illustrate the above general concepts, FIG. 1 is a schematic of theconversion of a composition 100 to a matrix 106 including a dispersionof semiconductor structures 104, such as quantum dots, therein, inaccordance with an embodiment of the present invention. Referring toFIG. 1, the composition 100 includes a plurality of discrete prepolymermolecules or ceramic precursor molecules 102 (designated as “M”) alongwith a plurality of the semiconductor structures 104. Upon modificationof the composition 100, the resulting matrix 106 is a polymer matrix ora ceramic matrix, respectively. The modification may be performed by,e.g., use of an initiator, a catalyst, appropriate reaction conditionssuch as heating, or combinations thereof. The matrix 106 can include apolymeric or long range molecular network 108 and can, possibly,included modified portions 102′ of the prepolymer molecules or ceramicprecursor molecules 102, as depicted in FIG. 1. In a specificembodiment, the composition 100 has a low viscosity while the matrix 106has a relatively high viscosity, generating a controlled dispersion ofthe semiconductor structures 104. As described in greater detail below,examples of reaction pathways include, but are not limited to, sol-gel(silanol condensation) pathways, polymerization (e.g., acrylic, epoxy)or side group (beta) elimination (thermal or photo-curing). Otherexamples include, but are not limited to, the use of metal-oxideprecursors other than silicon oxide such as aluminosilicate (zeolites)or diethoxysiloxane-ethyltitanate as a titania-silicate aerogel ormetal-chalcogenides such as zinc sulfide (ZnS).

Using the above general approach, in an embodiment, very thin, denselayers of QDs can be formed on an LED chip. Additionally, the generationof a stable dispersion and ready-to-apply formulation with longshelf-life can be achieved. Furthermore, a procedure for generating aprotective matrix and enhance performance of QDs incorporated thereinunder operating condition can be realized, while aggregation of harmfulcompounds from reaching the QD surfaces can be prevented. In aparticular example, nano-particles are dispersed in a small-molecularmedium which has the ability to load a higher amount of particulates permass unit of resulting polymer and, then a homogeneous nano-composite isgenerated. The dispersion can be further applied on the LED chip in athin layer followed by curing which can immobilize the nano-compositeson the surface yet permit flowing of the polymer at higher temperatures.

More specifically, nano-particles (with or without a silica shelling)are dispersed in a concentrated solution of a monomer (e.g., smallmolecules able to react with each other to generate polymers). Themonomers can be selected from a class of cyclosiloxanes as, describedbelow. An optionally included solvent can be selected for suitability asa dispersant for both monomer and polymer and to not induceprecipitation or aggregation of nano-particles. An amount of initiatorcan be added suitable to dictate the final molecular weight of thepolymer. The reaction can be permitted for a controlled amount of time(e.g., 1 hour) and terminated with a small molecule that reacts with theactive centers (e.g., an alcohol). Alternatively, nano-particles can bedispersed in small molecular or oligomeric compounds containing reactiveorgano-metallic sites. The organic moieties are eliminated under certainconditions (e.g., temperature, moisture, UV-light) to yield a curedinorganic matrix (metal-oxides). To the above dispersions, across-linker or catalyst, or both, can be added using 1 or 2-partformulation. Components can depend on the type of curing to be used. Forexample, if a vinyl cyclosiloxane is used as a monomer, the formulationcan include a multifunctional hydrosilane and a Pt based catalyst. Theformulations may be designed depending on curing protocols which can betriggered by moisture or other condensation processes, UV-light ortemperature. Ideally, the dispersion is used without furtherpurification for chip coating using deposition methods such as spraying,dip-coating, spin-coating or drop-casting.

In a first general aspect, compositions having a dispersion ofnano-particles therein and methods of fabricating compositions having adispersion of nano-particles therein from small molecule prepolymers aredescribed. Overall, in a general embodiment as illustrated in FIG. 1, amixture 100 of semiconductor nano-particles 104 and discrete prepolymermolecules 102 is formed. A polymer matrix 106 is then formed from thediscrete prepolymer molecules 102. The polymer matrix 106 includes adispersion of the semiconductor nano-particles 104 therein. In one suchembodiment, the discrete prepolymer molecules are cyclic monomers, andforming the polymer matrix involves opening the cyclic monomers with aninitiator species by adding the initiator species to the mixture. Inanother embodiment, the mixture and the polymer matrix are formed attemperatures approximately in the range of 20-30 degrees Celsius. In yetanother embodiment, the polymer matrix is formed from the discreteprepolymer molecules by using an approach such as, but not limited to, asilanol condensation sol-gel reaction, an acrylic or epoxy basedpolymerization reaction, a thermal β-elimination reaction, or aphoto-β-elimination reaction.

FIG. 2 illustrates a reaction pathway where a polysiloxane matrix 202 isformed by ring-opening of cyclic monomers 200, such as cyclosiloxanes,in accordance with an embodiment of the present invention. In one suchembodiment, opening the cyclic monomers 200 with the initiator speciesinvolves using a chain growth mechanism. In that case, a chain growthtermination species can be added to the mixture a duration of timesubsequent to adding the initiator species to the mixture. In anothersuch embodiment, additional cyclic monomers are added to the mixturesubsequent to adding the initiator species to the mixture.

As depicted in FIG. 2, the cyclic monomers 200 can be cyclic siloxanemonomers of the formula —[Si(R)(R′)—O]_(n)—, where, in an embodiment, nis 3, 4, 5 or 6, and where R or R′ is a ligand such as, but not limitedto, H, Cl, an alkyl radical with 1-8 carbon atoms, a fluoroalkyl of 3-8carbon atoms, allyl, vinyl, or combinations thereof. In an embodiment,the added initiator species is an electrophile such as, but not limitedto, an alkali metal hydroxide, an alkoxide, or a tetraalkylammoniumsilanolate. In a specific embodiment, subsequent to adding the initiatorspecies to the mixture, the mixture is quenched with water, an alcohol,or a functional disiloxane. As an example, the mixture can be quenchedis approximately 1-6 hours after adding the initiator species to themixture.

A mixture of semiconductor structures and discrete prepolymer molecules,such as cyclic monomers 200, can further include a solvent. In one suchembodiment, a suspension of the semiconductor nano-particles anddiscrete prepolymer molecules is formed in a solvent such as, but notlimited to, toluene, ethyl benzene, tetrahydrofuran, hexane, orcyclohexane. However, in another embodiment, the mixture ofsemiconductor nano-particles and discrete prepolymer molecules is formedin the absence of a solvent. In an embodiment, the mixture and, hence,the resulting polymer matrix, are formed in an acid-free environment. Inyet another embodiment, the mixture and, hence, the resulting polymermatrix, are formed under anhydrous conditions.

In a second general aspect, ceramic compositions having a dispersion ofnano-particles therein and methods of fabricating ceramic compositionshaving a dispersion of nano-particles therein from ceramic precursormolecules are described. Overall, in a general embodiment, as is alsoillustrated in FIG. 1, a mixture 100 of semiconductor nano-particles 104and ceramic precursor molecules 102 is formed. A ceramic matrix 106 isthen formed from the ceramic precursor molecules 102. The ceramic matrix106 includes a dispersion of the semiconductor nano-particles 104therein.

In an exemplary embodiment, the ceramic precursor molecules 102 arediscrete molecules. The resulting ceramic matrix 106 is an infiniteinorganic network. FIGS. 3A-3D are schematics of reactions involving theformation of a ceramic matrix of an infinite inorganic network as formedfrom discrete ceramic precursor molecules, in accordance with anembodiment of the present invention. Specifically, referring to FIG. 3A,the discrete molecules 102 are metal alkoxide molecules 300. The metalalkoxide molecules 300 undergo hydration 302 to provide active species304 formation. The active species 304 undergo a condensation reaction306 to provide a condensed active species 308, as depicted in FIG. 3B.Then, referring to FIG. 3C, the condensed active species 308 undergo solformation 310 to provide polycondensed sol active species 312. Thepolycondensed sol active species 312 are cross-linked through hydrolysis314, and the resulting species 316 is heated 318 to form a gel 320, asdepicted in FIG. 3D. The gel 320 is an infinite inorganic network (suchas 106) thus formed from hydrolysis of metal alkoxide molecules viahydrolyzed intermediate species.

Referring again to FIGS. 3A-3D, overall, metal-oxides synthesis bysol-gel process may be broken out in several stages or, alternatively,the reactions can proceed essentially simultaneously following thereaction of FIG. 3A. Nonetheless, the final product is an infiniteinorganic (e.g., ceramic) polymer network. It is to be understood thatone of the RO groups can be replace by H or an organic group (e.g.,methyl, vinyl) for ceramic structure and functionality variation. Also,the starting materials can include a hybrid or mixture of silane withother metal-alkoxides (e.g., sec-butixyaluminooxytriethoxysilane ordi-isopropoxy-di-(trimethylsiloxy)titanate).

In another embodiment, a ceramic matrix 106 is formed from linear metaloxide polymers or metal-oxide copolymers, e.g., they are formedessentially from a process using only the reaction described inassociation with FIG. 3D, where the actual ceramic matrix synthesisbegins with a linear species. Examples of such precursors include, butare not limited to, polyalkoxysiloxanes (e.g., with methyl or ethylligands), diethoxysiloxane, diethoxysiloxane-s-butylaluminate copolymer,poly(dibutyl titanate), or diethoxysiloxane-ethyltitanate copolymer.FIG. 4 is a schematic of reactions involving the formation of a ceramicmatrix of an infinite inorganic network as formed from linear ceramicprecursor molecules, in accordance with an embodiment of the presentinvention. Referring to FIG. 4, infinite metal-oxide 406 synthesis fromlinear precusrors 400 is performed by a sol-gel process involving alight (e.g., ultra-violet (UV)) or thermal (e.g., T>180 degrees Celsius)initiation process 402 and subsequent hydration process 404 throughintermediate species 499.

Referring again to FIGS. 3A-3D and 4, in an embodiment, the ceramicprecursor molecules are metal ceramic precursor molecules, and formingthe ceramic matrix involves catalyzing the metal ceramic precursormolecules to form a metal oxide matrix. In one such embodiment, a metalsilicate matrix such as, but not limited to, an aluminosilicate matrixor a titaniasilicate matrix is formed. In one embodiment, the metalceramic precursor molecules are catalyzed to form the metal oxide matrixby adding a strong base to the starting mixture. In another embodiment,the metal ceramic precursor molecules are catalyzed to form the metaloxide matrix by heating the mixture. In yet another embodiment, themetal ceramic precursor molecules are catalyzed to form the metal oxidematrix by exposing the mixture to ultra-violet (UV) light. It is to beunderstood that, in alternative embodiments, the ceramic precursormolecules are non-metal ceramic precursor molecules, and forming theceramic matrix involves catalyzing the non-metal ceramic precursormolecules to form a silica matrix.

In either case (metal or non-metal), in a specific embodiment, a ceramicmatrix is formed by using precursors having thermal and/or UV labilepolysilsequioxane with β-electron withdrawing groups, e.g., acetoxy,chloro, or bromo. Such an approach yields silica-rich structures.Exposure to UV light or temperatures of 180° C. and up can be used toperform the reactions with suitable reaction rates. However, a lowertemperature conversion can be facilitated in the presence of a fluorinesalt, including catalysts such as tetrabutylammonium fluoride.

In another embodiment, the ceramic precursor molecules 102 are metal ormetal-organic clusters. The use of such clusters can provide synthesisof ceramic matrices by an entirely inorganic, rapid, low-volume losscondensation pathway to provide homogeneous films of the ceramicmatrices. In other embodiments, however, the ceramic precursor molecules102 are polymeric. For example, in a specific embodiment, the polymericceramic precursor molecules are linear metal oxide polymers, and formingthe ceramic matrix involves forming a metal oxide matrix viacross-linking mechanisms, such as described in association with FIG. 4.

A mixture of semiconductor structures and ceramic precursor molecules,such as metal alkoxides 300, can further include a solvent. In one suchembodiment, a suspension of the semiconductor nano-particles and ceramicprecursor molecules is formed in a solvent such as, but not limited to,toluene, ethyl benzene, tetrahydrofuran, hexane, or cyclohexane.However, in another embodiment, the mixture of semiconductornano-particles and ceramic precursor molecules is formed in the absenceof a solvent. In an embodiment, the mixture and, hence, the resultingceramic matrix, are formed in an acid-free environment. In yet anotherembodiment, the mixture and, hence, the resulting ceramic matrix, areformed under aqueous conditions. In an alternative embodiment, however,the mixture and, hence, the resulting ceramic matrix, are formed underanhydrous conditions.

In another aspect, the above described compositions, or compositionprecursors, having a dispersion of nano-particles therein can includehetero-structure-based nano-particles, such as hetero-structure-basedquantum dots. Such hetero-structures may have specific geometriessuitable for performance optimization. In an example, several factorsmay be intertwined for establishing an optimized geometry for a quantumdot having a nano-crystalline core and nano-crystalline shell pairing.As a reference, FIG. 5 illustrates a schematic of a cross-sectional viewof a quantum dot suitable for dispersion in a composition or compositionprecursor, in accordance with an embodiment of the present invention.Referring to FIG. 5, a semiconductor structure (e.g., a quantum dotstructure) 500 includes a nano-crystalline core 502 surrounded by anano-crystalline shell 504. The nano-crystalline core 502 has a lengthaxis (_(aCORE)), a width axis (_(bCORE)) and a depth axis (_(cCORE)),the depth axis provided into and out of the plane shown in FIG. 5.Likewise, the nano-crystalline shell 504 has a length axis (_(aSHELL)),a width axis (_(bSHELL)) and a depth axis (_(cSHELL)), the depth axisprovided into and out of the plane shown in FIG. 5. The nano-crystallinecore 502 has a center 503 and the nano-crystalline shell 504 has acenter 505. The nano-crystalline shell 504 surrounds thenano-crystalline core 502 in the b-axis direction by an amount 506, asis also depicted in FIG. 5.

The following are attributes of a quantum dot that may be tuned foroptimization, with reference to the parameters provided in FIG. 5, inaccordance with embodiments of the present invention. Nano-crystallinecore 502 diameter (a, b or c) and aspect ratio (e.g., a/b) can becontrolled for rough tuning for emission wavelength (a higher value foreither providing increasingly red emission). A smaller overallnano-crystalline core provides a greater surface to volume ratio. Thewidth of the nano-crystalline shell along 506 may be tuned for yieldoptimization and quantum confinement providing approaches to controlred-shifting and mitigation of surface effects. However, strainconsiderations must be accounted for when optimizing the value ofthickness 506. The length (a_(SHELL)) of the shell is tunable to providelonger radiative decay times as well as increased light absorption. Theoverall aspect ratio of the structure 500 (e.g., the greater ofa_(SHELL)/b_(SHELL) and a_(SHELL)/c_(SHELL)) may be tuned to directlyimpact PLQY. Meanwhile, overall surface/volume ratio for 500 may be keptrelatively smaller to provide lower surface defects, provide higherphotoluminescence, and limit self-absorption. Referring again to FIG. 5,the shell/core interface 508 may be tailored to avoid dislocations andstrain sites. In one such embodiment, a high quality interface isobtained by tailoring one or more of injection temperature and mixingparameters, the use of surfactants, and control of the reactivity ofprecursors, as is described in greater detail below.

In accordance with an embodiment of the present invention, a high PLQYquantum dot is based on a core/shell pairing using an anisotropic core.With reference again to FIG. 5, an anisotropic core is a core having oneof the axes a_(CORE), b_(CORE) or c_(CORE) different from one or both ofthe remaining axes. An aspect ratio of such an anisotropic core isdetermined by the longest of the axes a_(CORE), b_(CORE) or c_(CORE)divided by the shortest of the axes a_(CORE), b_(CORE) or c_(CORE) toprovide a number greater than 1 (an isotropic core has an aspect ratioof 1). It is to be understood that the outer surface of an anisotropiccore may have rounded or curved edges (e.g., as in an ellipsoid) or maybe faceted (e.g., as in a stretched or elongated tetragonal or hexagonalprism) to provide an aspect ratio of greater than 1 (note that a sphere,a tetragonal prism, and a hexagonal prism are all considered to have anaspect ratio of 1 in keeping with embodiments of the present invention).

A workable range of aspect ratio for an anisotropic nano-crystallinecore for a quantum dot may be selected for maximization of PLQY. Forexample, a core essentially isotropic may not provide advantages forincreasing PLQY, while a core with too great an aspect ratio (e.g., 2 orgreater) may present challenges synthetically and geometrically whenforming a surrounding shell. Furthermore, embedding the core in a shellcomposed of a material different than the core may also be used enhancePLQY of a resulting quantum dot.

Accordingly, in an embodiment, a semiconductor structure includes ananisotropic nano-crystalline core composed of a first semiconductormaterial and having an aspect ratio between, but not including, 1.0 and2.0. The semiconductor structure also includes a nano-crystalline shellcomposed of a second, different, semiconductor material at leastpartially surrounding the anisotropic nano-crystalline core. In one suchembodiment, the aspect ratio of the anisotropic nano-crystalline core isapproximately in the range of 1.01-1.2 and, in a particular embodiment,is approximately in the range of 1.1-1.2. In the case of rounded edges,then, the nano-crystalline core may be substantially, but not perfectly,spherical. However, the nano-crystalline core may instead be faceted. Inan embodiment, the anisotropic nano-crystalline core is disposed in anasymmetric orientation with respect to the nano-crystalline shell, asdescribed in greater detail in the example below.

Another consideration for maximization of PLQY in a quantum dotstructure is to provide an asymmetric orientation of the core within asurrounding shell. For example, referring again to FIG. 5, the center503 of the core 502 may be misaligned with (e.g., have a differentspatial point than) the center 505 of the shell 504. In an embodiment, asemiconductor structure includes an anisotropic nano-crystalline corecomposed of a first semiconductor material. The semiconductor structurealso includes a nano-crystalline shell composed of a second, different,semiconductor material at least partially surrounding the anisotropicnano-crystalline core. The anisotropic nano-crystalline core is disposedin an asymmetric orientation with respect to the nano-crystalline shell.In one such embodiment, the nano-crystalline shell has a long axis(e.g., a_(SHELL)), and the anisotropic nano-crystalline core is disposedoff-center along the long axis. In another such embodiment, thenano-crystalline shell has a short axis (e.g., b_(SHELL)), and theanisotropic nano-crystalline core is disposed off-center along the shortaxis. In yet another embodiment, however, the nano-crystalline shell hasa long axis (e.g., a_(SHELL)) and a short axis (e.g., b_(SHELL)), andthe anisotropic nano-crystalline core is disposed off-center along boththe long and short axes.

With reference to the above described nano-crystalline core andnano-crystalline shell pairings, in an embodiment, the nano-crystallineshell completely surrounds the anisotropic nano-crystalline core. In analternative embodiment, however, the nano-crystalline shell onlypartially surrounds the anisotropic nano-crystalline core, exposing aportion of the anisotropic nano-crystalline core, e.g., as in a tetrapodgeometry or arrangement. In an embodiment, the nano-crystalline shell isan anisotropic nano-crystalline shell, such as a nano-rod, thatsurrounds the anisotropic nano-crystalline core at an interface betweenthe anisotropic nano-crystalline shell and the anisotropicnano-crystalline core. The anisotropic nano-crystalline shell passivatesor reduces trap states at the interface. The anisotropicnano-crystalline shell may also, or instead, deactivate trap states atthe interface.

With reference again to the above described nano-crystalline core andnano-crystalline shell pairings, in an embodiment, the first and secondsemiconductor materials (core and shell, respectively) are eachmaterials such as, but not limited to, Group II-VI materials, GroupIII-V materials, Group IV-VI materials, Group I-III-VI materials, orGroup II-IV-VI materials and, in one embodiment, are mono-crystalline.In one such embodiment, the first and second semiconductor materials areboth Group II-VI materials, the first semiconductor material is cadmiumselenide (CdSe), and the second semiconductor material is one such as,but not limited to, cadmium sulfide (CdS), zinc sulfide (ZnS), or zincselenide (ZnSe). In an embodiment, the semiconductor structure furtherincludes a nano-crystalline outer shell at least partially surroundingthe nano-crystalline shell and, in one embodiment, the nano-crystallineouter shell completely surrounds the nano-crystalline shell. Thenano-crystalline outer shell is composed of a third semiconductormaterial different from the first and second semiconductor materials. Ina particular such embodiment, the first semiconductor material iscadmium selenide (CdSe), the second semiconductor material is cadmiumsulfide (CdS), and the third semiconductor material is zinc sulfide(ZnS).

With reference again to the above described nano-crystalline core andnano-crystalline shell pairings, in an embodiment, the semiconductorstructure (i.e., the core/shell pairing in total) has an aspect ratioapproximately in the range of 1.5-10 and, 3-6 in a particularembodiment. In an embodiment, the nano-crystalline shell has a long axisand a short axis. The long axis has a length approximately in the rangeof 5-40 nanometers. The short axis has a length approximately in therange of 1-5 nanometers greater than a diameter of the anisotropicnano-crystalline core parallel with the short axis of thenano-crystalline shell. In a specific such embodiment, the anisotropicnano-crystalline core has a diameter approximately in the range of 2-5nanometers. The thickness of the nano-crystalline shell on theanisotropic nano-crystalline core along a short axis of thenano-crystalline shell is approximately in the range of 1-5 nanometersof the second semiconductor material.

With reference again to the above described nano-crystalline core andnano-crystalline shell pairings, in an embodiment, the anisotropicnano-crystalline core and the nano-crystalline shell form a quantum dot.In one such embodiment, the quantum dot has a photoluminescence quantumyield (PLQY) of at least 90%. Emission from the quantum dot may bemostly, or entirely, from the nano-crystalline core. For example, in anembodiment, emission from the anisotropic nano-crystalline core is atleast approximately 75% of the total emission from the quantum dot. Anabsorption spectrum and an emission spectrum of the quantum dot may beessentially non-overlapping. For example, in an embodiment, anabsorbance ratio of the quantum dot based on absorbance at 400nanometers versus absorbance at an exciton peak for the quantum dot isapproximately in the range of 5-35.

In an embodiment, a quantum dot based on the above describednano-crystalline core and nano-crystalline shell pairings is adown-converting quantum dot. However, in an alternative embodiment, thequantum dot is an up-shifting quantum dot. In either case, a lightingapparatus may include a light emitting diode and a plurality of quantumdots such as those described above. The quantum dots may be appliedproximal to the LED and provide down-conversion or up-shifting of lightemitted from the LED. Thus, semiconductor structures according to thepresent invention may be advantageously used in solid state lighting.The visible spectrum includes light of different colors havingwavelengths between about 380 nm and about 780 nm that are visible tothe human eye. An LED will emit a UV or blue light which isdown-converted (or up-shifted) by semiconductor structures describedherein. Any suitable ratio of emission color from the semiconductorstructures may be used in devices of the present invention. LED devicesaccording to embodiments of the present invention may have incorporatedtherein sufficient quantity of semiconductor structures (e.g., quantumdots) described herein capable of down-converting any available bluelight to red, green, yellow, orange, blue, indigo, violet or othercolor. These structures may also be used to downconvert or upconvertlower energy light (green, yellow, etc) from LED devices, as long as theexcitation light produces emission from the structures.

The above described semiconductor structures, e.g., quantum dots,suitable for inclusion as a dispersion in a composition or compositionprecursor may be fabricated to further include one or more compositionaltransition layers between portions of the structures, e.g., between coreand shell portions. Inclusion of such a transition layer may reduce oreliminate any performance inefficiency associated with otherwise abruptjunctions between the different portions of the structures. For example,the inclusion of a compositional transition layer may be used tosuppress Auger recombination within a quantum dot structure. Augerrecombination events translate to energy from one exciton beingnon-radiatively transferred to another charge carrier. Suchrecombination in quantum dots typically occurs on sub-nanosecond timescales such that a very short multi-exciton lifetime indicatesnon-radiative recombination, while higher nanosecond bi-excitonlifetimes indicate radiative recombination. A radiative bi-exciton has alifetime approximately 2-4 times shorter than radiative single exciton.

More specifically, as is described in greater detail below inassociation with FIGS. 6-8, an optimal particle (e.g., quantum dotstructure) may have one or more of a high aspect ratio, a large volumerelative to other quantum dot hetero-structures, and graded or alloyedtransitions between different semiconductor materials. The graded oralloyed transitions can be used to render a compositional and structuraltransition from one component (such as a quantum dot core) to anothercomponent (such as a quantum dot shell) a smooth function rather than astep function. In one embodiment, the terms “graded,” “gradient,” or“grading” are used to convey gradual transitioning from onesemiconductor to another. In one embodiment, the terms “alloy,”“alloyed,” or “alloying” are used to convey an entire volume having afixed intermediate composition. In more specific embodiments, core orseed volume is maximized relative to shell volume for a given emissioncolor. A graded or alloyed core/shell transition layer may be includedbetween the two volumes.

In a first example, FIG. 6 illustrates a cross-sectional view of asemiconductor structure having a nano-crystalline core andnano-crystalline shell pairing with one compositional transition layer,in accordance with an embodiment of the present invention.

Referring to FIG. 6, a semiconductor structure 600 includes anano-crystalline core 602 composed of a first semiconductor material. Anano-crystalline shell 604 composed of a second, different,semiconductor material at least partially surrounds the nano-crystallinecore 602. A compositional transition layer 610 is disposed between, andin contact with, the nano-crystalline core 602 and nano-crystallineshell 604. The compositional transition layer 610 has a compositionintermediate to the first and second semiconductor materials.

In an embodiment, the compositional transition layer 610 is an alloyedlayer composed of a mixture of the first and second semiconductormaterials. In another embodiment, the compositional transition layer 610is a graded layer composed of a compositional gradient of the firstsemiconductor material proximate to the nano-crystalline core 602through to the second semiconductor material proximate to thenano-crystalline shell 604. In either case, in a specific embodiment,the compositional transition layer 610 has a thickness approximately inthe range of 1.5-2 monolayers.

Exemplary embodiments include a structure 600 where the firstsemiconductor material is cadmium selenide (CdSe), the secondsemiconductor material is cadmium sulfide (CdS), and the compositionaltransition layer 610 is composed of CdSe_(x)S_(y), where 0<x<1 and0<y<1, or where the first semiconductor material is cadmium selenide(CdSe), the second semiconductor material is zinc selenide (ZnSe), andthe compositional transition layer 610 is composed of Cd_(x)Zn_(y)Se,where 0<x<1 and 0<y<1.

In accordance with an embodiment of the present invention, thecompositional transition layer 610 passivates or reduces trap stateswhere the nano-crystalline shell 604 surrounds the nano-crystalline core602. Exemplary embodiments of core and/or shell parameters include astructure 600 where the nano-crystalline core 602 is an anisotropicnano-crystalline core having an aspect ratio between, but not including,1.0 and 2.0 (in a specific embodiment, approximately in the range of1.01-1.2), and the nano-crystalline shell is an anisotropicnano-crystalline shell having an aspect ratio approximately in the rangeof 4-6.

In an embodiment, the nano-crystalline shell 604 completely surroundsthe nano-crystalline core 602, as depicted in FIG. 6. In an alternativeembodiment, however, the nano-crystalline shell 604 only partiallysurrounds the nano-crystalline core 602, exposing a portion of thenano-crystalline core 602. Furthermore, in either case, thenano-crystalline core 602 may be disposed in an asymmetric orientationwith respect to the nano-crystalline shell 604. In one or moreembodiments, semiconductor structures such as 600 are fabricated tofurther include a nano-crystalline outer shell 606 at least partiallysurrounding the nano-crystalline shell 604. The nano-crystalline outershell 606 may be composed of a third semiconductor material differentfrom the first and second semiconductor materials, i.e., different fromthe materials of the core 602 and shell 604. The nano-crystalline outershell 606 may completely surround the nano-crystalline shell 604 or mayonly partially surround the nano-crystalline shell 604, exposing aportion of the nano-crystalline shell 604.

For embodiments including a nano-crystalline outer shell, an additionalcompositional transition layer may be included. Thus, in a secondexample, FIG. 7 illustrates a cross-sectional view of a semiconductorstructure having a nano-crystalline core/nano-crystallineshell/nano-crystalline outer shell combination with two compositionaltransition layers, in accordance with an embodiment of the presentinvention.

Referring to FIG. 7, a semiconductor structure 700 includes thenano-crystalline core 602, nano-crystalline shell 604, nano-crystallineouter shell 606 and compositional transition layer 610 of structure 600.However, in addition, semiconductor structure 700 includes a secondcompositional transition layer 712 disposed between, and in contactwith, the nano-crystalline shell 604 and the nano-crystalline outershell 606. The second compositional transition layer 712 has acomposition intermediate to the second and third semiconductormaterials, i.e., intermediate to the semiconductor materials of theshell 604 and outer shell 606.

In an embodiment, the second compositional transition layer 712 is analloyed layer composed of a mixture of the second and thirdsemiconductor materials. In another embodiment, the second compositionaltransition layer 712 is a graded layer composed of a compositionalgradient of the second semiconductor material proximate to thenano-crystalline shell 604 through to the third semiconductor materialproximate to the nano-crystalline outer shell 606. In either case, in aspecific embodiment, the second compositional transition layer 712 has athickness approximately in the range of 1.5-2 monolayers. Exemplaryembodiments include a structure 700 where the first semiconductormaterial is cadmium selenide (CdSe), the second semiconductor materialis cadmium sulfide (CdS), the third semiconductor material is zincsulfide (ZnS), and the second compositional transition layer 1412 iscomposed of Cd_(x)Zn_(y)S, where 0<x<1 and 0<y<1, or the firstsemiconductor material is cadmium selenide (CdSe), the secondsemiconductor material is zinc selenide (ZnSe), the third semiconductormaterial is zinc sulfide (ZnS), and the second compositional transitionlayer 1412 is composed of ZnSe_(x)S_(y), where 0<x<1 and 0<y<1. Inaccordance with an embodiment of the present invention, the secondcompositional transition layer 712 passivates or reduces trap stateswhere the nano-crystalline outer shell 606 surrounds thenano-crystalline shell 604.

For other embodiments including a nano-crystalline outer shell, an outercompositional transition layer may be included without including aninner compositional transition layer. Thus, in a third example, FIG. 8illustrates a cross-sectional view of a semiconductor structure having anano-crystalline core/nano-crystalline shell/nano-crystalline outershell combination with one compositional transition layer, in accordancewith an embodiment of the present invention.

Referring to FIG. 8, a semiconductor structure 800 includes thenano-crystalline core 602, nano-crystalline shell 604, andnano-crystalline outer shell 606 of structure 600. In addition, thesemiconductor structure 800 includes the compositional transition layer712 of structure 700 disposed between, and in contact with, thenano-crystalline shell 604 and the nano-crystalline outer shell 606.However, structure 800 does not include the compositional transitionlayer 610 of structure 600, i.e., there is no compositional transitionlayer between the core 602 and shell 604.

Referring to FIGS. 5-8, and as depicted in FIGS. 6-8, the structures500, 600, 700 and 800 may further include an insulator coating (e.g.,shown as 608 in FIGS. 6-8) surrounding and encapsulating thenano-crystalline core/nano-crystalline shell pairing or nano-crystallinecore/nano-crystalline shell/nano-crystalline outer shell combination. Inone such embodiment, the insulator coating is composed of an amorphousmaterial such as, but not limited to, silica (SiO_(x)), titanium oxide(TiO_(x)), zirconium oxide (ZrO_(x)), alumina (AlO_(x)), or hafnia(HfO_(x)). In an embodiment, insulator-coated structures based onstructures 500, 600, 700 and 800 are quantum dot structures. Forexample, structures 500, 600, 700 and 800 may be used as adown-converting quantum dot or an up-shifting quantum dot.

The above described insulator coating may be formed to encapsulate aquantum dot using a reverse micelle process. For example, FIG. 9illustrates operations in a reverse micelle approach to coating asemiconductor structure, in accordance with an embodiment of the presentinvention. Referring to part A of FIG. 9, a quantum dot hetero-structure(QDH) 902 (e.g., a nano-crystalline core/shell pairing) has attachedthereto a plurality of TOPO ligands 904 and TOP ligands 906. Referringto part B, the plurality of TOPO ligands 904 and TOP ligands 906 areexchanged with a plurality of Si(OCH₃)₃(CH₂)₃NH₂ ligands 908. Thestructure of part B is then reacted with TEOS (Si(OEt)₄) and ammoniumhydroxide (NH₄OH) to form a silica coating 910 surrounding the QDH 902,as depicted in part C of FIG. 9.

In another aspect, a composition, such as composition 100 from FIG. 1,or a resulting matrix, such as matrix 106 from FIG. 1, is applied to alighting device to provide a layer having a dispersion of semiconductorstructures therein for inclusion in the lighting device. Thecompositions or resulting matrices can be those as described above inassociation with FIGS. 1-4. In one embodiment, the dispersion ofsemiconductor structures is a dispersion of quantum dots such as thosedescribed above in association with FIGS. 5-8.

In a first exemplary embodiment, a method of applying a light-conversionlayer to a surface of a light-emitting diode (LED) includes first,separately, forming a polymer matrix or a ceramic matrix from a mixtureof quantum dots and discrete prepolymer molecules or ceramic precursormolecules, respectively. The resulting polymer matrix or ceramic matrixincludes a dispersion of the quantum dots therein and is then applied tothe surface of the LED. In one such embodiment, applying the polymermatrix or ceramic matrix to the surface of the LED involves using atechnique such as, but not limited to, spraying, dip-coating,spin-coating, or drop-casting. The polymer matrix or the ceramic matrixcan be cured with ultra-violet (UV) light exposure or heating, in oneembodiment.

In a second exemplary embodiment, a method of applying alight-conversion layer to a surface of a light-emitting diode (LED)includes first applying a mixture of quantum dots and discreteprepolymer molecules or ceramic precursor molecules to the surface ofthe LED. A polymer matrix or a ceramic matrix is then formed from themixture of quantum dots and discrete prepolymer molecules or ceramicprecursor molecules, respectively, on the surface of the LED. Theresulting polymer matrix or ceramic matrix includes a dispersion of thequantum dots therein. In one such embodiment, applying the mixture ofquantum dots and discrete prepolymer molecules or ceramic precursormolecules to the surface of the LED involves using a technique such as,but not limited to, spraying, dip-coating, spin-coating, ordrop-casting. Forming the polymer matrix or the ceramic matrix,respectively, there from can involve curing the mixture of quantum dotsand discrete prepolymer molecules or ceramic precursor molecules withultra-violet (UV) light exposure or heating, in one embodiment. Ineither example, it is to be understood that the matrix or matrixprecursors can be applied to discrete LED devices or, in anotherembodiment, prior to dicing the LED from a wafer having a plurality ofLED dies. In the latter case, application of the matrix or matrixprecursors may be distributed uniformly across the wafer prior to dicingthe wafer.

With respect to illustrating the above concepts in a resulting deviceconfiguration, FIG. 10 illustrates a lighting device 1000. Device 1000has a blue LED 1002 with a layer 1004 having a dispersion of quantumdots 1006 therein, in accordance with an embodiment of the presentinvention. Devices 1000 may be used to produce “cold” or “warm” whitelight. In one embodiment, the device 1000 has little to no wasted energysince there is little to no emission in the IR regime. In a specificsuch embodiment, the use of a layer having a composition with adispersion of anisotropic quantum dots therein enables greater thanapproximately 40% lm/W gains versus the use of conventional phosphors.Increased efficacy may thus be achieved, meaning increased luminousefficacy based on lumens (perceived light brightness) per wattelectrical power. Accordingly, down converter efficiency and spectraloverlap may be improved with the use of a dispersion of quantum dots toachieve efficiency gains in lighting and display. In an additionalembodiment, a conventional phosphor is also included in the composition,along with the dispersion of quantum dots 1006.

Different approaches may be used to provide a quantum dot layer in alighting device. In an example, FIG. 11 illustrates a cross-sectionalview of a lighting device 1100 with a layer having a composition with adispersion of quantum dots therein, in accordance with an embodiment ofthe present invention. Referring to FIG. 11, a blue LED structure 1102includes a die 1104, such as an InGaN die, and electrodes 1106. The blueLED structure 1102 is disposed on a coating or supporting surface 1108and housed within a protective and/or reflective structure 1110. A layer1112 is formed over the blue LED structure 1102 and within theprotective and/or reflective structure 1110. The layer 1112 has acomposition including a dispersion of quantum dots or a combination of adispersion of quantum dots and conventional phosphors. Although notdepicted, the protective and/or reflective structure 1110 can beextended upwards, well above the matrix layer 1112, to provide a “cup”configuration.

In another example, FIG. 12 illustrates a cross-sectional view of alighting device 1200 with a layer having a composition with a dispersionof quantum dots therein, in accordance with another embodiment of thepresent invention. Referring to FIG. 12, the lighting device 1200includes a blue LED structure 1202. A quantum dot down converter screen1204 is positioned somewhat remotely from the blue LED structure 1202.The quantum dot down converter screen 1204 includes a layer with acomposition having a dispersion of quantum dots therein, e.g., ofvarying color, or a combination of a dispersion of quantum dots andconventional phosphors. In one embodiment, the device 1200 can be usedto generate white light, as depicted in FIG. 12.

In another example, FIG. 13 illustrates a cross-sectional view of alighting device 1300 with a layer having a composition with a dispersionof quantum dots therein, in accordance with another embodiment of thepresent invention. Referring to FIG. 13, the lighting device 1300includes a blue LED structure 1302 supported on a substrate 1304 whichmay house a portion of the electrical components of the blue LEDstructure 1302. A first conversion layer 1306 has a composition thatincludes a dispersion of red-light emitting anisotropic quantum dotstherein. A second conversion layer 1308 has a second composition thatincludes a dispersion of quantum dots or green or yellow phosphors or acombination thereof (e.g., yttrium aluminum garnet, YAG phosphors)therein. Optionally, a sealing layer 1310 may be formed over the secondconversion layer 1308, as depicted in FIG. 13. In one embodiment, thedevice 1300 can be used to generate white light.

In another example, FIG. 14 illustrates a cross-sectional view of alighting device 1400 with a layer having a composition with a dispersionof quantum dots therein, in accordance with another embodiment of thepresent invention. Referring to FIG. 14, the lighting device 1400includes a blue LED structure 1402 supported on a substrate 1404 whichmay house a portion of the electrical components of the blue LEDstructure 1402. A single conversion layer 1406 has a composition thatincludes a dispersion of red-light emitting anisotropic quantum dots incombination with a dispersion of green quantum dots or green and/oryellow phosphors therein. Optionally, a sealing layer 1410 may be formedover the single conversion layer 1406, as depicted in FIG. 14. In oneembodiment, the device 1400 can be used to generate white light.

In additional examples, FIGS. 15A-15C illustrate cross-sectional viewsof various configurations for lighting devices 1500A-1500C with a layerhaving a composition with a dispersion of quantum dots therein,respectively, in accordance with another embodiment of the presentinvention. Referring to FIGS. 15A-15C, the lighting devices 1500A-1500Ceach include a blue LED structure 1502 supported on a substrate 1504which may house a portion of the electrical components of the blue LEDstructure 1502. A conversion layer 1506A-1506C, respectively, has acomposition that includes a dispersion of one or more light-emittingcolor types of quantum dots therein. Referring to FIG. 1500Aspecifically, the conversion layer 1506A is disposed as a thin layeronly on the top surface of the blue LED structure 1502. Referring toFIG. 1500B specifically, the conversion layer 1506B is disposed as athin layer conformal with all exposed surfaces of the blue LED structure1502. Referring to FIG. 1500C specifically, the conversion layer 1506Cis disposed as a “bulb” only on the top surface of the blue LEDstructure 1502. In the above examples (e.g., FIGS. 10-14 and 15A-15C),although use with a blue LED is emphasized, it is to be understood thata layer having a composition with a dispersion of quantum dots thereincan be used with other light sources as well, including LEDs other thanblue LEDs.

In another aspect, a composition such as composition 100 from FIG. 1 isa storable composition. As one possibility described above, the storablecomposition can be maintained until application to, e.g., a lightingdevice, is sought. The application to the lighting device can includemodification of the composition to a matrix having a dispersion ofsemiconductor structures, e.g., quantum dots, therein, such as formationof matrix 106 of FIG. 1.

In a first example, in an embodiment, such a composition includes amedium made up of or including discrete prepolymer molecules. The mediumis a liquid at 25 degrees Celsius (e.g., at room temperature). Aplurality of semiconductor nano-particles is suspended in the medium. Inone such embodiment, the discrete prepolymer molecules are cyclicmonomers. In a specific such embodiment, the cyclic monomers are cyclicsiloxane monomers of the formula —[Si(R)(R′)—O]_(n)—, where n is 3, 4, 5or 6, and where R or R′ is a ligand such as, but not limited to, H, Cl,an alkyl radical with 1-8 carbon atoms, a fluoroalkyl of 3-8 carbonatoms, allyl, vinyl, or combinations thereof. The medium can furtherinclude a solvent. In one embodiment, the solvent is one such as, butnot limited to, toluene, ethylbenzene, tetrahydrofuran, hexane, orcyclohexane. However, in an alternative embodiment, the medium issolvent-free. As described above, in an embodiment, the semiconductornano-particles are quantum dots.

In a second example, in another embodiment, such a composition includesa medium made up of or including ceramic precursor molecules. The mediumis a liquid or gel at 25 degrees Celsius (e.g., at room temperature). Aplurality of semiconductor nano-particles is suspended in the medium. Inone such embodiment, the ceramic precursor molecules are discretemolecules. In another such embodiment, the ceramic precursor moleculesare linear metal oxide polymers. In yet another such embodiment, theceramic precursor molecules are thermal or ultra-violet (UV) labilepolysilsequioxane molecules having one or more β-electron withdrawinggroups. The medium can further include a solvent. In one embodiment, thesolvent is one such as, but not limited to, toluene, ethylbenzene,tetrahydrofuran, hexane, or cyclohexane. However, in an alternativeembodiment, the medium is solvent-free. As described above, in anembodiment, the semiconductor nano-particles are quantum dots.

Thus, ceramic compositions having a dispersion of nano-particles thereinand methods of fabricating ceramic compositions having a dispersion ofnano-particles therein have been disclosed.

What is claimed is:
 1. A method of applying a light-conversion layer toa surface of a light-emitting diode (LED), the method comprising:applying a mixture of quantum dots and discrete ceramic precursormolecules to the surface of the LED, wherein the quantum dots arehetero-structure quantum dots having an outer insulator coating alreadyformed thereon prior to forming the mixture, wherein the outer insulatorcoating comprises a layer of material selected from the group consistingof silica (SiO_(x)), titanium oxide (TiO_(x)), zirconium oxide(ZrO_(x)), alumina (AlO_(x)), and hafnia (HfO_(x)), and wherein thediscrete ceramic precursor molecules are thermal or ultra-violet (UV)labile polysilsequioxane molecules having one or more β-electronwithdrawing groups; and subsequent to applying the mixture of quantumdots and discrete ceramic precursor molecules to the surface of the LED,forming, from the mixture, a ceramic matrix on the surface of the LED,the ceramic matrix comprising a dispersion of the quantum dots therein,wherein forming the ceramic matrix comprises forming a silica-rich orsilicate matrix via heating or UV-light exposure.
 2. The method of claim1, wherein applying the mixture to the surface of the LED comprisesusing a technique selected from the group consisting of spraying,dip-coating, spin-coating, and drop-casting.
 3. The method of claim 1,wherein the quantum dots each comprise an anisotropic nano-crystallinecore comprising a first semiconductor material and having an aspectratio between, but not including, 1.0 and 2.0, and a nano-crystallineshell comprising a second, different, semiconductor material at leastpartially surrounding the anisotropic nano-crystalline core.
 4. Themethod of claim 1, wherein the quantum dots each comprise anano-crystalline core comprising a first semiconductor material, anano-crystalline shell comprising a second, different, semiconductormaterial at least partially surrounding the nano-crystalline core, and acompositional transition layer disposed between, and in contact with,the nano-crystalline core and nano-crystalline shell, the compositionaltransition layer having a composition intermediate to the first andsecond semiconductor materials.
 5. The method of claim 1, wherein thequantum dots each comprise a nano-crystalline core comprising a firstsemiconductor material, a nano-crystalline shell comprising a second,different, semiconductor material at least partially surrounding thenano-crystalline core, a nano-crystalline outer shell at least partiallysurrounding the nano-crystalline shell, the nano-crystalline outer shellcomprising a third semiconductor material different from the first andsecond semiconductor materials, and a compositional transition layerdisposed between, and in contact with, the nano-crystalline shell andthe nano-crystalline outer shell, the compositional transition layerhaving a composition intermediate to the second and third semiconductormaterials.
 6. The method of claim 1, wherein the mixture of quantum dotsand discrete ceramic precursor molecules is applied to the surface ofthe LED prior to dicing the LED from a wafer comprising a plurality ofLED dies.
 7. The method of claim 1, wherein forming the ceramic matrixcomprises forming a silica-rich matrix.
 8. The method of claim 1,wherein forming the ceramic matrix comprises forming a silicate matrix.9. The method of claim 1, wherein forming the ceramic matrix comprisesforming the forming silica-rich or silicate matrix via heating.
 10. Themethod of claim 1, wherein forming the ceramic matrix comprises formingthe forming silica-rich or silicate matrix via UV-light exposure. 11.The method of claim 1, wherein the outer insulator coating comprises alayer of silica (SiO_(x)).
 12. The method of claim 1, wherein the outerinsulator coating comprises a layer of titanium oxide (TiO_(x)).
 13. Themethod of claim 1, wherein the outer insulator coating comprises a layerof zirconium oxide (ZrO_(x)).
 14. The method of claim 1, wherein theouter insulator coating comprises a layer of alumina (AlO_(x)).
 15. Themethod of claim 1, wherein the outer insulator coating comprises a layerof hafnia (HfO_(x)).